It was on February 19 that police briefly arrested the former prince on suspicion of misconduct in public office and searched his residences at the royal family's country estate of Sandringham and in Windsor.
His lawyers have questioned whether the operation was legal, and a judge has now ruled that Thames Valley Police made serious errors in their application for a search warrant.
Andrew Mountbatten-Windsor denies the allegations, which are linked to the Epstein affair.
